High-torque potentiometer



April 25, 1961 c. YOURA 2,981,914

HIGH-TORQUE POTENTIOMETER Filed March 5. 1959 INVENTOR. 07/47/915)" VdMF/l United States Patent HIGH-TORQUE POTENTIOMETER Charles Youra, Van Nuys, Calif., assignor to Technology Instrument Corporation of Acton, a corporation of Massachusetts Filed Mar. 3, 1959, Ser. No. 796,844

4 Claims. (Cl. 338-162) This invention relates to rotary potentiometers and more particularly to high-torque rotary potentiometers.

As used herein, the term high-torque rotary potentiometer denotes a rotary potentiometer having an operating shaft that can be turned only when subjected to a relatively high amount of torque. Potentiometers of this type, sometimes called trimming potentiometers, are used where it is desired that a selected setting not be disturbed by shock orvibration.

The primary object of this invention is to provide a rotary potentiometer having novel means for applying continuously a gripping force on its operating shaft, whereby a positive relatively strong manually applied force is required to turn the shaft.

A more specific object is to provide a high-torque rotary potentiometer comprising a rotatable operating shaft and a pair of springs held in tight frictional engagement with the shaft and exerting thereon a force which can be overcome only by a relatively high torque.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a side view, partly in section, of a rotary potentiometer embodying the present invention;

Fig. 2 is a cross-sectional view taken along line 22 of Fig. l; and

Fig. 3 is a cross-sectional view taken along line 3-3 of Fig. 1.

Referring now to Fig. 1, there is shown a rotary potentiometer comprising a cylindrical casing 2 having a removable end wall 4 at one end and a fixed wall 6 at the other end. Extending around and adhesively secured to the interior of casing 2 is a conventional wound wire resistance element 8.

End wall 6 has a central hole 10 in which is fixedly secured a bushing 12. This bushing comprises three I integral cylindrical sections 14, 16, and 18 of different inside diameters. The intermediate cylindrical section 16 functions as a bearing collar to rotatably support an operating shaft 20 whose inner end extends into casing 2.

Securely attached to the inner end of shaft 2 is a split collar 22 which carries a radially extending arm 24. A screw 25 is used to secure collar 22 to the shaft. The radially extending arm 24 supports a resilient contact 26 which slidingly engages resistance element 8. Although not shown, it is to be understood that the ends of resistance element 8 are connected by suitable means to two fixed input terminals carried by casing 2 and that contact 26 is connected by additional means to a third output terminal carried by casing 2. Such connections and terminals are old as shown, for example, by US. Patent No. 2,778,906, issued January 22, 1957, to L. M. Burgess, and are omitted from the drawings solely to better emphasize the novel features of the invention.

The inner surface of bushing portion 18 has a semicylindrical groove 28 which is in alignment with and forms an extension of a bore 30 formed in intermedi ate portion 16. A pin 32 is seated in bore 30 and extends through the length of groove 28. The outer end of shaft 20 is of stepped construction, comprising a first enlarged portion 34 which is smaller in diameter than the inside diameter of bushing portion 18 and a sec-- ond enlarged portion 36 which is larger than the first portion 34. The outer surface of shaft portion 34 has a semi-cylindrical groove 40 which is in alignment with and forms an extension of a bore 42 formed in the enlarged portion 36. A second pin 44 is seated in bore 42 and extends through the length of groove 40. Pin 44 terminates just short of the outer end surface of the intermediate portion 16 of the bushing. Pins 32 and 44 are force-fitted in bushing 12 and shaft 20 respectively and are made of rigid metal stock. These pins cooperate to limit movement of shaft 20 to a few degrees less than a full revolution. This is accomplished by virtue of their engagement with one another as shown in Fig. 2. This stop mechanism forms no part of the present invention and is disclosed simply to illustrate how a stop mechanism may be embodied in a potentiometer which also includes the present invention.

The present invention comprises the use of a pair of flat metal springs 50 and 52 which have a length greater than a chord of the circle outlined by the inner surface of bushing portion 14 which is tangent to shaft 20. In the illustrated embodiment, they are approximately equal in length to the inside diameter of bushing portion 14. These springs are forced into bushing portion 14 on opposite sides of shaft 20 and are spaced from bushing section 16 by an annular spacer 54 which abuts bushing section 16 and surrounds shaft 20. Because of their length, springs 50 and 52 must be bent in order to fit within the bushing. The ends of the springs are held in tight engagement with the interior surface of bushing portion 14 by the edging force exerted on the springs intermediate their ends by shaft 20. The springs in turn exert a clamping force on the shaft, holding it against rotation.

The springs are held in place by an annular plug 60 which surrounds shaft 20 and is force-fitted in the end of bushing section 14. Plug 60 does not impede rotation of shaft 20. An O-ring 62 attached to shaft 20 acts against the end of plug 60 to prevent axial movement of shaft 20 away from casing 2. The enlarged portion 34 of the shaft acts against bushing portion 16 to prevent axial movement toward the casing.

With the foregoing construction, a relatively high amount of torque is required to turn shaft 20 to shift contact 26 to a new position on resistance element 8. To facilitate turning the shaft, the outer end 36 is kerfed as at 64 to accommodate a screwdriver bit.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. Therefore, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts specifically described or illustrated, and that within the scope of the appended claims, it may be practiced otherwise than as specifically described or illustrated.

I claim:

1. In a rotary potentiometer comprising a casing, a circular resistance element supported in said casing, a shaft having one end extending into said casing, said shaft having an arm on said one end provided with a wiper element in sliding engagement with said resistance element, and means supporting said shaft in rotatable relation with said casing, the improvement comprising a pair of fiat spring elements spaced from each other by said shaft, and means urging said spring elements into tight frictional engagement with said shaft at substantially diametrically opposed points, whereby to prevent rotation of said shaft.

2. In a rotary potentiometer comprising a casing, a

resistance element in said casing, a shaft having a con-- tact element for picking voltages ofi of said resistance element, and means supporting said shaft in rotatable relation with said casing, the improvement comprising a pair of separate flat spring elements spaced from each other by said shaft, and means urging said spring elements into tight frictional engagement with said shaft at two different points located in a common plane running transversely to said shaft, whereby to hold said shaft against rotation.

3. The combination of claim 2 wherein said shaft-sup porting means and said spring-urging means are integral with and form part of a bushing mounted in said casing.

4. In a rotary potentiometer having a casing containing a resistance element and a rotatable operating shaft having a wiper element for etfecting contact with said resistance element at different points along the length of said resistance element, the improvement comprising a bushing attached to said casing having a first inner cylindrical surface rotatably supporting said shaft and a second inner cylindrical surface in coaxial and spaced relation to said shaft, and a pair of separate flat spring elements positioned within said bushing and spaced from each other by said shaft, said second surface in tight engagement with the ends of said spring elements and urging said spring elements into tight frictional engagement with said shaft whereby to hold said shaft against rotation.

References Cited in the file of this patent UNITED STATES PATENTS 1,641,396 7 Norviel Sept. 6, 1927 

